Method of manufacturing multilayer circuit substrate

ABSTRACT

A method of manufacturing a multilayer circuit substrate includes a process of forming via holes in an insulating film, a process of applying an electrically conducting paste obtained by having ultra-fine metal particles disperse in a solvent onto an insulating film, and a process of forming vias composed of a sintered product of ultra-fine metal particles in the via holes by removing the solvent and also sintering the ultra-fine metal particles. The sintered products of the ultra-fine metal particles on the insulating layer is removed (or patterned) by peeling off the protective film stuck to the insulating layer.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of manufacturing a multilayercircuit substrate, and more particularly to a method of manufacturing amultilayer circuit substrate having a structure that multilevelinterconnections are connected with each other through vias.

2. Description of the Prior Art

As an electronic computer becomes higher in operation speed and asemiconductor device becomes larger in capacity and becomes more highlyintegrated, a method of packaging of a semiconductor device on asubstrate has also been changed to a large extent.

In a thin film multilayer circuit substrate, high density packaging,fine interconnection, multilayer formation or the like have become themainstream, and a plurality of interconnections (conductors) have becometo be formed in a small space. Further, in order to achieve high-speedpropagation of a signal, it has become indispensable to reduce parasiticcapacity by using an insulating film of low dielectric constant.

A thin film multilayer circuit substrate is obtainable by repeating sucha process that an interconnection is formed on the insulating film, aninsulating film is formed further thereon, and an interconnection isformed on the insulating film. In this case, a conductive via is formedin an interlayer insulating film in order to connect an upperinterconnection and a lower interconnection with each otherelectrically.

A general process of forming vias is as described hereunder. First,photosensitive resin is used as an interlayer insulating film, thisphotosensitive resin is applied onto a substrate, and then via holes areformed in the photosensitive resin through exposure and development, andthe patterned photosensitive resin layer is cured by heating to apredetermined temperature to form an insulating layer. Then, conductivelayers are formed on the cured photosensitive resin (or insulatinglayer) and in the via holes by sputtering, plating or the like. Theconductive layers in the via holes become vias, and the conductivelayers on the cured insulating layer of the photosensitive resin areformed into patterns so as to become interconnections.

A circuit substrate is formed into a multilayer by repeating such aprocess as formation of the interlayer insulating films and formation ofvia holes, vias and interconnections.

In the process of forming via holes in the photosensitive resin thatbecomes an interlayer insulating film after curing, however, such laboras exposure, development, and curing is required. Further, it forms thevia configuration into a step shape to form the via by sputtering orplating, thus causing the via to show a thin layer partially. Suchformation of the via into a thin film now incurs high resistance of thevia and now causes disconnection at the connecting part between the viaand the interconnection.

When photolithography is used in order to form an interconnection on theinterlayer insulating film, the throughput of forming the thin filmmultilayer circuit substrate is decreased. Further, according to aprocess of photolithography, it is impossible to achieve furtherminiaturization of the via and formation of higher aspect ratio of thevia, and to meet the requirements for high density packaging, fineinterconnection, formation of a multilayer or the like attendant uponachievement of high speed of an electronic computer. As to a method offorming an interconnection, a method of having conductive ultra-fineparticles project on an insulating film from a nozzle while moving thenozzle, thereby to draw interconnections composed of ultra-fineparticles is described in Japanese Patent Provisional Publication No.HEI5-136128 for instance. According to this method, it is impossible toincrease the moving speed of the nozzle for the purpose of eliminatingconfiguration defects of the interconnections, and the throughput offorming the interconnections is decreased.

On the other hand, in a conventional thin film multilayer circuitsubstrate, such a process that an insulating film is formed, via holesare formed in the insulating film, a conductive material is filled inthe via holes thereafter so as to form vias and the interconnection isfurther formed, is repeated a plurality of times sometimes. Since astress is applied to an interlayer due to heating, patterning or thelike performed whenever the insulating film and the conductive film arelaminated repeatedly according to this process, these films become topeel off each other more easily.

Thereupon, a method of manufacturing a multilayer circuit substrate bypreparing in advance a plurality of insulating films in which vias areformed and interconnections are formed on the upper surface and crimpingthese plurality of insulating films with heating in a state that theyare placed one upon another in order to obtain good connection ofmultilevel interconnections is described in Japanese Patent ProvisionalPublication No. HEI5-152755. According to this method, however, sincethe vias are made to project from the insulating film, a gap becomesliable to be produced in the periphery of the vias and there is a fearthat adhesion between insulating films is lowered when the number ofvias is large.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method ofmanufacturing a multilayer circuit substrate for improving thethroughput, forming a fine via having a high aspect ratio and alsomaking it difficult to produce exfoliation between layers.

According to the present invention, a process of forming aninterconnection pattern on an insulating film and filling vias in viaholes in the insulating film by using electrically conductive pastehaving ultra-fine metal particles is included. Ultra-fine metalparticles are supplied in a uniform thickness within the via holes byusing the paste in which ultra-fine metal particles are contained.Accordingly, the via formed by sintering ultra-fine metal particlesshows almost uniform thickness even when the aspect ratio is madelarger, thus showing good connection between the via and theinterconnection.

When photosensitive resin is used for the material of the insulatinglayer, the via holes are formed through exposure and development.Further, when an insulating layer applicable with laser processing isused, the via holes are formed by laser abrasion. With the laser, it ispossible to form a via hole having a large aspect ratio and a smalldiameter as compared with the case that the photosensitive resin isused.

By heating ultra-fine metal particles in vacuum for sintering, a solventin the paste is removed and air bubbles in a sintered product ofultra-fine metal particles are also removed. The ultra-fine metalparticles are burned at a lower temperature (approximately 300° C.). Thethroughput is improved by using the sintered product of the ultra-finemetal particles left on the insulating layer as an interconnectionmaterial as it is. The material of the ultra-fine metal particles isgold, copper, silver, palladium, nickel or the like.

Further, according to a thin film multilayer circuit substrate of thepresent invention, the vias composed of sintered products of ultra-finemetal particles are left in the via holes by forming a protective filmon an insulating layer, forming holes for vias in the protective filmand the insulating film, applying paste having ultra-fine metalparticles on the protective film and in the holes hereafter, andthereafter, by removing the solvent in the paste, sintering theultra-fine metal particles and then peeling off the protective film fromthe insulating layer.

With this, the process of removing the sintered product of theultra-fine metal particles from the top of the insulating film issimplified. Besides, the protective film is formed of a material thathas a high heat resisting temperature and is easily adhered and peeledoff in a state of a film.

Furthermore, since opening portions are formed along the interconnectionpattern in the protective film in addition to the holes for vias, thesintered product of the ultra-fine metal particles filled in the openingportions remains on the insulating film by peeling off the protectivefilm. Since the sintered product of the ultra-fine metal particles onthe insulating film is used as the interconnection, the interconnectionand the via are formed at the same time, thus further improving thethroughput.

According to another aspect of the present invention, a plurality oflayers in which vias and interconnections are formed in or on theinsulating films are formed in advance, these layers are placed one uponanother so as to connect vias with interconnections, and resin (such asepoxy resin) is filled thereafter in gaps between layers (or films) by apotting method, thereby to connect between layers (or films).

It makes the stress generated between layers smaller and eliminates agap between layers around the projections of the vias to fill the gapbetween layers with resin such as epoxy resin (such as epoxy resin),thus improving adhesion between layers.

In another aspect of the present invention, a first film composed of onemetal or several of metals selected from groups composed of, forinstance, nickel (Ni), gold (Au), palladium (Pd), and silver (Ag), etc.is formed first in an area where an electrode on a substrate surface isto be formed, and a second film composed of, for instance, copper (Cu),etc. is formed in other areas. Then, after a conductor or conductivepaste film is formed by applying a conductor paste obtained bydispersing ultra-fine metal particles in a solvent onto those first andsecond films, heat treatment is applied so as to vaporize solventcomponents in the paste film and also to form a metal film composed ofsintered products of the ultra-fine metal particles. According to thepresent invention, since ultra-fine metal particle each having aparticle diameter as small as 10 nm or less for instance are used ascompared with that each of the metal particles in conventionalconductive paste has a diameter as large as approximately 20 μm,ultra-fine metal particles are sintered easily at a comparatively lowtemperature of 250° C. at the lower limit (preferably approximately 300°C.), thus making it possible to obtain a metal film.

Thereafter an adhesive tape is stuck onto the metal film, and theadhesive tape is peeled off thereafter. In this case, since the adhesionof a metal film of gold or the like to a film of nickel or the like isstrong, and the adhesion of a metal film of gold or the like to a filmof copper or the like is weak, the metal film on the second Cu film isremoved being adhered to the adhesive tape, and only the metal film onthe first Ni film remains.

In such a manner, according to the present invention, a film of gold orthe like is formed on the back of the electrode by means of liftoffmethod. As a result, complicated process such as plating pretreatmentand plating waste liquid process is unnecessary, and it is possible toform a surface electrode easily.

Further, in yet another method of manufacturing a semiconductor deviceof the present invention, paste obtained by dispersing ultra-fine metalparticles in a solvent is used for junction between a bonding land and asemiconductor chip. Since ultra-fine metal particles are used, thispaste is sintered by applying heat treatment at a comparatively lowtemperature of 250° C. at the lower limit (preferably approximately 300°C.), thus making it possible to bond a semiconductor chip to a bondingland firmly. With this, it is possible to fix a chip to a bonding landfirmly, thus making die-bonding of excellent thermal conductivity, ohmicjunction and thermal stress absorptivity possible due to the lowertemperature bonding.

Besides, when an organic solvent having low viscosity such asα-terpineol is used as a solvent, the paste spreads thinly and uniformlyin a gap between the chip and the bonding land by a capillary phenomenonwhen the chip is placed on the bonding land. With this, it is surelyavoidable that the chip is inclined with respect to the substratesurface.

Further, the above ultra-fine metal particles comprise metal particleshaving an average particle diameter of 100 nm or less and 5 nm or more.

The sintering process is performed in the nitrogen atmosphere or thehydrogen atmosphere or the air. The palladium sintering process is notperformed in the hydrogen atmosphere.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A to 1E are sectional views showing a process of manufacturing amultilayer circuit substrate according to a first embodiment of thepresent invention;

FIGS. 2A to 2E are sectional views showing a process of manufacturing amultilayer circuit substrate according to a second embodiment of thepresent invention;

FIGS. 3A to 3E are sectional views showing a process of manufacturing amultilayer circuit substrate according to a third embodiment of thepresent invention;

FIGS. 4A to 4E are sectional views showing a process of manufacturing amultilayer circuit substrate according to a fourth embodiment of thepresent invention;

FIGS. 5A to 5F are sectional views showing a process of manufacturing amultilayer circuit substrate according to a fifth embodiment of thepresent invention;

FIGS. 6A to 6C are sectional views showing a process of manufacturing amultilayer circuit substrate according to a sixth embodiment of thepresent invention;

FIGS. 7A to 7G are sectional views showing a method of manufacturing asemiconductor device according to a seventh embodiment of the presentinvention.

FIGS. 8A to 8G are sectional views showing a method of manufacturing asemiconductor device according to an eighth embodiment of the presentinvention.

FIGS. 9A to 9G are sectional views showing a method of manufacturing asemiconductor device according to a ninth embodiment of the presentinvention.

FIGS. 10A to 10C are sectional views showing a method of manufacturing asemiconductor device according to a tenth embodiment of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(The first embodiment)

A process of manufacturing a multilayer interconnection circuitsubstrate according to a first embodiment of the present invention willbe described with reference to FIGS. 1A to 1E.

First, as shown in FIG. 1A, an interconnection 2 in a first layer isformed on a substrate 1 composed of aluminum nitride, silicon or thelike directly or through an insulating film (not shown). Thereafter, aninsulating film 3 having a thickness of approximately 20 μm and amelting temperature of 300° C. or higher is formed on the substrate 1,thereby to cover the interconnection 2 in the first layer with theinsulating film 3. When polyimide is used as the material of theinsulating film 3, polyimide precursor solution is spin-coated on thesubstrate 1, which is heated and solidified so as to form the insulatingfilm 3.

Thereafter, as shown in FIG. 1B, a protective film 4 composed ofthermoplastic polyimide for instance having a thickness of approximately20 μm is stuck on the insulating film 3. As the thermoplastic polyimide,one that has heat resistance of 300° C. or higher and is adhered orpeeled off easily in a state of a film is used. As concrete materials,for example, a trade name AURUM (manufactured by Mitsui ToatsuChemicals, Inc.), a trade name LARC-TPI (manufactured by Mitsui ToatsuChemicals, Inc./NASA), a trade name ULTEM (manufactured by GE) and so onare available.

Next, as shown in FIG. 1C, the protective film 4 and the insulating film3 located in a via forming region on the interconnection 2 in the firstlayer are irradiated with excimer laser, thereby to form a via hole 5 ina size of 20×20 μm² in the insulating film 3. When the excimer laser isradiated, a mask (not shown) in which a via pattern is formed is used.

Then, after irradiating energy of the excimer laser is lowered, theprotective film 4 is irradiated with excimer laser along a pattern thatan interconnection in the second layer is going to be formed. With this,opening portions 6 along the interconnection in the second layer isformed in the protective film 4. When the excimer laser is radiated, amask (not shown) having an interconnection pattern is used.

Thereafter, as shown in FIG. 1D, electrically conductive paste 7 isapplied onto the protective film 4 in a thickness of 1 μm, and the paste7 is also filled in the via hole 5 and the opening portions 6. The pasteis obtained by making ultra-fine metal particles of conductors such asgold and silver palladium alloy in an organic solvent such asα-terpineol.

Then, the substrate 1 is heated at a temperature of approximately 300°C. in a low-pressure ambient atmosphere so as to vaporize the organicsolvent in the paste 7, and the ultra-fine metal particles in the paste7 are also sintered while defoaming thereby to form them into a filmconfiguration. Since the diameter of one grain of ultra-fine metalparticles is approximately 50 nm for copper and approximately 10 nm forgold, they are sintered easily by heating at approximately 300° C. Sincethe pattern of the opening portion 6 collapses when the protective film4 is molten when the ultra-fine metal particles are sintered, it isrequired to select a material having a melting temperature higher thanthe sintering temperature as the material for the protective film 4.Accordingly, it is impossible to use the resist having heatingresistance of approximately 150° C. only in place of the protective film4.

Next, when the protective film 4 is peeled off from the insulating film3, only the pattern of ultra-fine metal particles remains on theinsulating film 3 as shown in FIG. 1E. Then, a via 8 composed of thesintered product of ultra-fine metal particles is formed in the via hole5 of the insulating film 3, and interconnections 9 in the second layercomposed of the sintered product of the ultra-fine metal particles areformed further on the insulating film 3. When a resin material is usedas the insulating film 3, good adhesion between the part of theinsulating film 3 irradiated with laser and the sintered product of theultra-fine metal particles is obtainable.

A multilayer interconnection circuit substrate is completed by repeatingthe process from which the insulating film 3 is formed until the via 8and the interconnections 9 are formed as described above a plurality oftimes (5 times for instance).

Besides, as the material of ultra-fine metal particles, copper, silver,palladium, nickel and so on are available in addition to gold andsilver-palladium alloy.

According to the present embodiment, the interconnection 9 is formed onthe insulating film 3 or the via 8 is filled in the via hole 5 by usingthe paste 7 containing ultra-fine metal particles. Therefore, the via 8that is formed by utilizing metal particles in a paste form scarcelyshow a step configuration even when the aspect ratio is made large, butthe step is very small even though a step configuration is produced.Therefore, the via 8 is neither made to show high resistance nordisconnected, thus obtaining good connection between the via 8 and theinterconnection 9.

Further, since the sintered product of ultra-fine metal particles formedon the insulating film 3 is used as the interconnection materials, itbecomes unnecessary to form a new interconnection material on theinsulating film 3, thus improving the throughput.

Further, useless sintered product of ultra-fine metal particles on theinsulating film 3 is removed by such a simple operation that theprotective film 4 is peeled off. Therefore, removal of resist and dryingtreatment become no longer required, and the process of filling theconductive material locally in the via hole 5 is simplified.

Furthermore, since the sintered product of the ultra-fine metalparticles is made to remain along the opening portion 6 of theprotective film 4, the pattern of the interconnections 9 in the secondlayer is formed by a simple work of peeling off the protective film 4.Therefore, resist removal and drying treatment become unnecessary, andthe forming process for interconnection patterning is simplified.Moreover, since the interconnections and the vias are applied withpatterning at the same time by exfoliation of the protective film 4, thethroughput is further improved.

Besides, the patterning by irradiation with laser is performed in ashort period of time as compared with a process of forming a conductivepattern by moving a nozzle for supplying conductive paste.

(The second embodiment)

A process of manufacturing a multilayer interconnection circuitsubstrate according to a second embodiment of the present invention willbe described with reference to FIGS. 2A to 2E.

First, as shown in FIG. 2A, an interconnection 12 in a first layer isformed on an insulating substrate 11 composed of glass or ceramics.Thereafter, an insulating film 13 having a thickness of approximately 20μm is formed on the substrate 11, and the interconnection 12 in thefirst layer is covered with the insulating film 13. When polyimide isused as the insulating film 13, polyimide precursor solution isspin-coated on the substrate 11, which is solidified by heating so as toform the insulating film 13.

Thereafter, as shown in FIG. 2B, the insulating film 13 is irradiatedwith excimer laser, thereby to form a via hole 14 as large as 20×20 μm²in the irradiated region. When excimer laser is irradiated, a mask (notshown) in which a via pattern has been formed is used.

Then, as shown in FIG. 2C, paste 15 obtained by having copper ultra-fineparticles dispersed in an organic solvent is applied in a thickness of 1μm onto the insulating film 13, and the paste 15 is filled sufficientlyin the via hole 14.

Furthermore, the organic solvent in the paste 15 is vaporized and thecopper ultra-fine particles in the paste 15 are also sintered whiledefoaming by heating the substrate 11 at a temperature of approximately300° C. in a low-pressure ambient atmosphere. With this, a via 16 isformed in the via hole 14 of the insulating film 13, and a conductivefilm 17 composed of copper is formed further on the insulating film 13.Besides, the insulating film 13 is formed of a material that is notmolten (flowed or deformed) by sintering

Next, as shown in FIG. 2D, resist 18 is applied onto the conductive film17, which is exposed and developed so as to leave the resist 18 at aportion where arrangement of the interconnection in the second layer ispredetermined. Then, the conductive film 17 is etched with the resist 18as a mask, thereby to form interconnections 19 in the second layer suchas shown in FIG. 2E. As an etchant of the conductive film 17 composed ofcopper, ammonium persulfate is used for instance.

A multilayer interconnection circuit substrate has been formed byrepeating the process until the insulating film 13, the via 16 and theinterconnection 19 are formed as described above five times in total forinstance.

According to the present embodiment, the interconnection 19 is formed onthe substrate 11 and the via 16 is formed in the via hole 14 by usingthe electrically conductive paste 15 having copper ultra-fine particles.Therefore, the fine via 16 is formed at a high aspect ratio similarly tothe first embodiment, and moreover, the via 16 is neither made high inresistance nor disconnected, thus obtaining good connection between thevia 16 and the interconnection 12, 19.

Further, since the sintered product of the ultra-fine particles thathave remained on the insulating film 13 is used as the interconnectionmaterial, the process of newly forming a conductive film becomesunnecessary, thus improving the throughput.

(The third embodiment)

A process of manufacturing a multilayer interconnection circuitsubstrate according to a third embodiment of the present invention willbe described with reference to FIGS. 3A to 3E.

First, as shown in FIG. 3A, an interconnection 22 in a first layer isformed on a substrate 21 composed of silicon directly or through aninsulating film (not shown). Thereafter, an insulating film 23 having athickness of approximately 20 μm is formed on the substrate 21, and theinterconnection 22 in the first layer is covered with the insulatingfilm 23. Polyimide is used for instance as the insulating film 23similarly to the first embodiment.

Thereafter, a protective film 24 having a thickness of approximately 20μm composed of thermoplastic polyimide for instance is stuck onto theinsulating film 23.

Next, as shown in FIG. 3B, the protective film 24 and the insulatingfilm 23 located at a partial region on the interconnection 22 in thefirst layer are irradiated with excimer laser so as to open a hole, anda via hole 25 in the size of 20×20 μm² for instance is formed in theinsulating film 23 located in the irradiated region similarly to thefirst embodiment.

Thereafter, as shown in FIG. 3C, electrically conductive paste 26obtained by having ultra-fine metal particles dispersed in an organicsolvent is applied onto the protective film 24, and the paste is filledin the via hole 25 at the same time. Then, the organic solvent in thepaste 26 is vaporized and the ultra-fine metal particles in the pasteare also sintered while defoaming so as to form a conductive layer byheating the substrate at a temperature of approximately 300° C. in alow-pressure ambient atmosphere. The insulating film 23 is formed of amaterial that is not molten (flowed) by sintering. Further, since theprotective film 24 is formed of a material having a high heat resistingtemperature, it will never melt when the ultra-fine metal particles aresintered. The material for the protective film 24 that is the same asthe one in the first embodiment is used.

Next, when the protective film 24 is peeled off, a via 27 composed of asintered product of the ultra-fine metal particles is formed in the viahole 25 of the insulating film 23 as shown in FIG. 3D.

Thereafter, a conductive film such as copper is formed on the insulatingfilm 23 and the via 27 by sputtering or the like, and then patterning isapplied to the conductive film by photolithography, thereby to forminterconnections 28 in the second layer such as shown in FIG. 3E.

A multilayer interconnection circuit substrate has been formed byrepeating the process of forming the insulating film 23 until the via 27and the interconnections 28 are formed as described above five times intotal.

According to the present embodiment, since the via 27 is formed in thevia hole 25 by using the paste 26 containing ultra-fine metal particlesas described above, the via 27 formed of the sintered product of theultra-fine metal particles scarcely shows a step configuration even whenthe aspect ratio is made large, and the step is very small even though astep configuration is formed. Accordingly, the via is protected fromgetting high in resistance and from being disconnected, thus obtaininggood connection between the via 27 and the interconnection 22 or 28.

Further, since the useless sintered product of the ultra-fine metalparticles on the insulating film 23 is removed by peeling off theprotective film 24 without performing etching, drying or the like, theprocess in the case of leaving the sintered product of the ultra-finemetal particles selectively in the via hole 25 is simplified.

(The fourth embodiment)

A process of manufacturing a multilayer interconnection circuitsubstrate according to a fourth embodiment of the present invention willbe described with reference to FIGS. 4A to 4E.

First, as shown in FIG. 4A, an interconnection 32 in a first layer isformed on a substrate 31 composed of silicon directly or through aninsulating film (not shown). Thereafter, an insulating film 33 having athickness of approximately 20 μm is formed on the substrate 31, and theinterconnection 32 in a first layer is covered with the insulating film33. Polyimide is used for instance as the insulating film 33 similarlyto the first embodiment.

Thereafter, a protective film 34 having a thickness of approximately 20μm composed of thermoplastic polyimide for instance is stuck onto theinsulating film 33. A material same as the one in the first embodimentis used as the material of the protective film.

Next, similarly to the first embodiment, the protective film 34 and theinsulating film 33 are irradiated with excimer laser so as to open ahole at a part on the interconnection 32 in the first layer, and a viahole 35 in a size of 20×20 μm² for instance is formed in the insulatingfilm 33 located in the irradiated region.

Thereafter, as shown in FIG. 4B, paste 36 obtained by having ultra-finemetal particles of conductors dispersed in an organic solvent is appliedonto the protective film 34, and the paste is also filled in the viahole 35. Then, the organic solvent in the paste 36 is vaporized and theultra-fine metal particles in the paste are also sintered whiledefoaming so as to form a conductive layer by heating the substrate at atemperature of approximately 300° C. in a low-pressure ambientatmosphere.

Next, when the protective film 34 is peeled off, a via 37 composed ofthe sintered product of ultra-fine metal particles is formed in the viahole 35 of the insulating film 33 as shown in FIG. 4C.

Thereafter, as shown in FIG. 4D, resist 38 is applied onto theinsulating film 33 and the via 37 and exposed and developed, thereby toform opening portions in the resist 38 along a portion where arrangementof the interconnection in the second layer is predetermined. Then, aconductive film 39 such as copper is formed by sputtering or the like,the resist 38 is removed further by a solvent, and the conductive film39 thereon is lifted off.

By this process, interconnections 40 in the second layer such as shownin FIG. 4E are formed on the insulating film 33.

A multilayer interconnection circuit substrate has been formed byrepeating the process from the formation of the insulating film 33 untilthe formation of the via 37 and the interconnections 40 as describedabove five times in total.

According to the present embodiment, since the via 37 is formed of asintered product of ultra-fine metal particles as described abovesimilarly to the third embodiment, the via 37 scarcely shows a stepconfiguration even when the aspect ratio of the via 37 is made large,and the step is very small even though a step configuration is produced.Thus, the via is prevented from getting high in resistance and frombeing disconnected, and good connection between the via 37 and theinterconnection 40 is obtainable.

Further, when the useless sintered product of the ultra-fine metalparticles on the insulating film 33 is removed, the protective film 34is peeled off only without performing etching, drying or the like.Therefore, the process in the case of leaving the sintered product ofthe ultra-fine metal particles in the via hole 35 selectively issimplified.

(The fifth embodiment)

A process of manufacturing a multilayer interconnection circuitsubstrate according to a fifth embodiment of the present invention willbe described with reference to FIGS. 5A to 5F.

First, as shown in FIG. 5A, a conductive film 42 having a three-layerstructure composed of titanium (Ti), nickel (Ni) and gold (Au) is formedby sputtering on one surface of a metallic foil 41 of copper (Cu) havinga film thickness of 20 μm. Ti is formed for the purpose of improvingadhesion with the metallic foil 41, and Ni is used as a barrier metal.Next, after a chrome (Cr) film 41a is formed by sputtering on themetallic foil 41 on the opposite side, polyimide of low dielectricconstant is applied in a thickness of approximately 20 μm, which isbaked so as to form an insulating film 44 (polyimde). The Cr film 41a isformed in order to improve adhesion between the polyimide and themetallic (Cu) foil 41.

Then, after a first resist 43 is formed on the conductive film 42 havinga three-layer structure (Ti/Ni/Au), a desired location of the insulatingfilm 44 is irradiated with excimer laser thereby to form via holes 45.

Thereafter, as shown in FIG. 5B, Sn--Pb solder plating is applied byelectrolytic plating using the metallic (Cu) foil 41 as the electrode soas to fill solder sufficiently in the via holes 45, and this solder isused as vias 46. The solder is plated extending over to slightprojection from the insulating film 44. Besides, since the conductivefilm 42 having a three-layer structure is covered by the first resist43, no solder plating is formed on the surface thereof.

Next, as shown in FIG. 5C, after the first resist 43 is removed byoxygen plasma, a second resist 47 is applied further to the conductivefilm 42 having a three-layer structure, and the resist 47 is exposed anddeveloped so as to form a pattern for interconnection. Then, theconductive film 42 having a three-layer structure (Ti/Ni/Au), the Crlayer 41a and the metallic (Cu) foil 41 are etched with the secondresist 47 as a mask, thereby to form interconnections 48 composed ofthese metals. (See FIG. 5D.)

A film 50 is formed with the insulating film 44, the vias 46 and theinterconnections 48 such as described above. A plurality of such films50 are prepared and placed one upon another while performing alignmenton the substrate 51 as shown in FIG. 5E. The patterns of theinterconnections 48 and the positions of the vias 46 of respectivelayers are made all the same in FIG. 5E for convenience sake, but theymay be made different with respect to each phase. Alignment is made atthe same time so that the interconnections 52 formed on the substrate 51such as aluminum nitride and the vias 46 of the films 50 lie one uponanother.

Thereafter, the vias 46 and the interconnections 48, 52 or the viasplaced thereon are connected mechanically and electrically by heating ata temperature at a melting point or higher of the solder materialconstituting the vias 46. Since solder is liable to get wet with Au ofthe conductive layer 42 having a three-layer structure (Ti/Ni/Au), thevias 46 are connected to the interconnections 48 and 52 easily.

The misalignment between the vias 46 and the interconnections 48 and 52or between the via 46 and the via 46 produced in alignment between thefilms 50 is corrected automatically by a self-alignment effect by thesurface tension of the molten solder.

Next, as shown in FIG. 5F, the substrate 51 and the insulating films 44connected through the interconnections 48 and 52 and the vias 46 areplaced in a low-pressure ambient atmosphere, and epoxy resin 53 isfilled by potting in the gap between the substrate 51 and the insulatingfilm 44 and the gaps between the insulating films 44. With this, amultilayer thin film circuit has been obtained.

In the above-mentioned embodiment, a plurality of insulating films 44 inwhich the vias 46 and the interconnections 48 are formed are prepared inadvance and these layers are placed one upon another so as to connectthe vias 46 and the interconnections 48 and 52 with one another, andepoxy resin 53 is filled thereafter by a potting method in the gapsamong the insulating films 44 and between the insulating film 44 and thesubstrate 51 so as to connect layers one another.

According to this method, since the stress generated between theinsulating films 44 becomes smaller, and moreover, epoxy resin is alsofilled around the projections of the vias 46, adhesion between layers orfilms 50 is improved. With this, adhesion between insulating layers 44and between the insulating film 44 and the substrate 51 is improved.

Besides, in the above description, the insulating film 44 formed on themetallic (Cu) foil 41 may be a film composed of resin having lowdielectric constant such as polyimide. In this case, the insulating film44 and the metallic (Cu) foil 41 are stuck to each other.

(The sixth embodiment)

A metallic foil is employed as a substrate, and a conductive film havinga three-layer structure (Ti/Ni/Au), a Cr film, an insulating film or thelike are laminated on top and bottom thereof in the fifth embodiment,but a multilayer structure may be formed with the insulating film as asubstrate.

For example, as shown in FIG. 6A, a Cr film 62 and a Cu film 63 areformed on a polyimide film 61 having a film thickness of 50 μm thatbecomes an insulating film, and a conductive film 64 having athree-layer structure of Ti, Ni and Au is formed thereafter. Thesemetallic layers are formed by sputtering for instance. The Cr film 62 isformed for the purpose of improving adhesion between the Cu film 63 andthe polyimide film 61, and in the conductive film 64 having athree-layer structure, Ti is formed for the purpose of improvingadhesion between the Cu film 63 and nickel, and Ni is used as a barriermetal.

Next, after first resist 65 is formed on the conductive film 64 having athree-layer structure, via holes 66 are formed in the polyimide film 61using excimer laser similarly to the fifth embodiment (FIG. 6B).

Then, as shown in FIG. 6C, vias 46 are formed in the via holes 66 withthe Cr film 62, the Cu film 63 and so on the polyimide film 61 as theelectrode. The vias 46 in this case are made to project slightly fromthe polyimide film 61.

This structure shows essentially the same structure as that shown inFIG. 5B, and thereafter, interconnections are formed along the processshown in the fifth embodiment, and the polyimide films 61 are furtherplaced one upon another in a plurality of layers, thereby to form amultilayer circuit substrate.

Besides, the polyimide film 61 corresponds to the insulating film 44 inthe fifth embodiment, and the Cu film 63 corresponds to the metallic(Cu) foil 41 in the fifth embodiment.

(The seventh embodiment)

FIGS. 7A to 7G are sectional views showing a method of manufacturing asemiconductor device according to a seventh embodiment of the presentinvention.

First, as shown in FIG. 7A, conductor patterns (interconnections, groundor the like) 102 composed of copper and insulating films 103 composed ofpolyimide are formed alternately on an aluminum nitride substrate 101,thereby to form a thin film multilayer circuit substrate 105. Via holes104 for connecting upper interconnections with lower interconnectionsare formed in the thin film multilayer circuit substrate 105.

This process is similar to a conventional process, and a well-knowntechnique can be used. When the conductor patterns 102 of the uppermostlayers are formed, however, the process is performed as follows. Namely,a conductor layer is formed on the whole surface of the insulating film103, a nickel film 106 is formed in a thickness of approximately 2 μm onthis conductor layer, and a patterned resist 99 is selectively formedthereafter. Then, the conductor patterns 102 of the uppermost layer areformed by etching the conductor layer with this resist as a mask.

Next, after a copper film 107 is formed on the whole surface of thesubstrate 105 by a vacuum evaporation method or the like, the resist ispeeled off. With this, as shown in FIG. 7B, it is possible to formcopper films 107 only on those areas on the surface of the thin filmmultilayer circuit substrate 105 where no nickel film 106 has beenformed. Besides, the film thickness of the copper film 107 is made to beapproximately 0.5 μm.

Next, as shown in FIG. 7C, paste obtained by dispersing ultra-fine goldparticles each having a particle diameter of approximately 10 nm into anorganic solvent is applied to the whole surface of the substrate 105 byspin coating for instance, thereby to obtain a paste film 108 having afilm thickness of approximately 1 μm.

Next, as shown in FIG. 7D, heat treatment is performed at approximately300° C. so as to vaporize the organic solvent in the paste film 108, andthe ultra-fine gold particles are also sintered, thus obtaining a goldfilm 109. The heat treatment may also be performed in a reduced pressureatmosphere in order to prevent air bubbles from generating in the goldfilm 109.

Since ultra-fine gold particles each having a particle diameter as smallas approximately 10 nm are used as ultra-fine metal particles, theparticles are sintered easily by heating at a temperature ofapproximately 300° C. in the heat treatment process. Besides, ultra-finecopper particles each having a particle diameter of approximately 50 nmmay also be used in place of the ultra-fine gold particles.

Next, as shown in FIG. 7E, after an adhesive tape 111 is stuck onto thegold film 109, the adhesive tape 111 is peeled off. Then, as shown inFIG. 7F, the gold film 109 that has adhered onto the nickel film 106remains, but the gold film 109 that has adhered onto the copper film 107is peeled off as it is adhered to the adhesive tape 111. This is becauseof such a reason that the adhesion of the gold film 109 to the copperfilm 107 is weak and the gold film 109 can be peeled off easy or readilywith the adhesive tape 111, whereas the adhesion of the gold film 109 tothe nickel film 106 is strong and the gold film 109 is not peeled offeasily with the adhesive tape 111.

Next, as shown in FIG. 7G, the copper films 107 at the portions exposedare etched with an ammonium persulfate aqueous solution, thereby toremove the copper films 107 among the gold film 109 patterned on thesurface of the substrate 105. With this, surface electrodes 110 eachmade of the gold film 109 on the surface thereof are completed. Forexample, surface electrodes 110 are used as a bonding pad.

According to the present embodiment, since it is possible to form theelectrode 110 having a gold film 109 easily without plating with gold,complicated processes such as plating pretreatment and plating wasteliquid treatment are not required, thus making it possible to form asurface electrode easily.

Besides, it is also conceivable that, after the gold film 109 is formedas described above, the gold film 109 is etched so as to have the goldfilm remain on the electrode surface only. In this case, aqua regia,cyanic etchant, iodine etchant or the like are available as the etchantfor gold. In an etching method, however, the electrode is side-etched orthe resist remains sometimes at dent portions in a pattern having dentsunless under optimum conditions. Thus, the etching method cannot be usedas to be the optimum method of forming the surface electrode. Althoughthere is no such a drawback in a liftoff method, resist cannot bear upagainst heat treatment when the ultra-fine metal particles are sinteredsince resin resist is used in a normal liftoff method.

In the present embodiment, since a film such as gold is applied withpatterning onto the electrode surface utilizing the difference betweenthe adhesion of the nickel film 106 to the ultra-fine metal particlefilm (the gold film 109) and the adhesion of the copper film 107 to theultra-fine metal particle film (the gold film 109), it is possible toform a surface electrode having a film of gold or the like on thesurface locally by the liftoff method without using resin resist.

(The eighth embodiment)

FIGS. 8A to 8G are sectional views showing a method of manufacturing asemiconductor device according to an eighth embodiment of the presentinvention.

First, as shown in FIG. 8A, conductor patterns 122 composed of copperand insulating films 123 composed of polyimide are formed alternately onan aluminum nitride substrate 121, thereby to form a thin filmmultilayer circuit substrate 125. Via holes 124 for connecting upperinterconnections to lower interconnections are formed in the thin filmmultilayer circuit substrate 125.

This process is similar to a conventional process, and a well-knowntechnique can be used. However, when a conductor pattern 122 in theuppermost layer is formed, the process is performed as follows. Namely,a conductor layer is formed on the whole surface of an insulating film123, a palladium film 126 is formed on the conductor layer in athickness of approximately 2 μm, and a pattern of resist 99 is formedthereafter. Then, the conductor pattern 122 of the uppermost layer isformed by etching the above-mentioned conductor layer with this resistas a mask.

Next, after a copper film 127 is formed on the whole surface of thesubstrate 125 by a vacuum evaporation method or the like, the resist ispeeled off. With this, as shown in FIG. 8B, it is possible to form thecopper film 127 only in the areas on the surface of the thin filmmultilayer circuit substrate 125 where the palladium film 126 is notformed. Besides, the film thickness of the copper film 127 is made to beapproximately 0.5 μm.

Next, as shown in FIG. 8C, a conductor paste obtained by dispersingultra-fine metal particles of gold and palladium each having a particlediameter of approximately 10 nm is applied onto the whole surface of thesubstrate 125 by spin coating for instance, thereby to form a conductorpaste film 128 in a thickness of approximately 1 μm.

Next, as shown in FIG. 8D, the substrate 125 and the conductor pastefilm 128 are heat-treated at approximately 300° C. so as to vaporize anorganic solvent in the conductor paste film 128 and the ultra-fine metalparticles of gold and palladium particles are sintered at the same time,thereby to obtain a gold-palladium alloy film 129. This heat treatmentmay also be performed in a reduced pressure atmosphere in order toprevent air bubbles from generating in the gold-palladium alloy film129. The ultra-fine metal particles of gold and palladium are sinteredeasily by heating at approximately 300° C.

Next, as shown in FIG. 8E, after an adhesive tape 111 is stuck onto thegold-palladium alloy film 129, the adhesive tape 111 is peeled off.Then, as shown in FIG. 8F, the gold-palladium film 129 that has adheredonto the palladium film 126 remains, but the gold-palladium film 129that has adhered onto the copper film 127 is peeled off as it is adheredto the adhesive tape 111. This is because of such a reason that theadhesion of the gold-palladium film 129 to the copper film 127 is weakand the gold-palladium film 129 can be peeled off simply with theadhesive tape 111, whereas the adhesion of the gold-palladium film 129to the palladium film 126 is strong and the film 129 is not peeled offeasily.

Then, as shown in FIG. 8G, the copper films 127 at the portions exposedare etched with an ammonium persulfate aqueous solution, thereby toremove the copper films 127 among conductor patterns 130 on the surfaceof the substrate 125. With this, surface electrodes 130 each having thegold-palladium alloy film 129 on the surface thereof are completed.

According to the present embodiment, complicated processes such asplating pretreatment and plating waste liquid treatment are notrequired, and it is possible to form an electrode having agold-palladium alloy film on the surface thereof easily.

(The ninth embodiment)

FIGS. 9A to 9G are sectional views showing a method of manufacturing asemiconductor device according to a ninth embodiment of the presentinvention.

First, as shown in FIG. 9A, conductor patterns 132 composed of copperand insulating films 133 composed of polyimide are formed alternately ona glass-ceramic substrate 131, thereby to form a thin film multilayercircuit substrate 135. Via holes 134 for connecting upperinterconnections to lower interconnections are formed in this thin filmmultilayer circuit substrate 135.

This process is similar to a conventional process, and a well-knowntechnique can be used. However, when the conductor pattern 132 of theuppermost layer is formed, the process is executed as follows. Namely, aconductor layer is formed on the whole surface of the insulating film133, a palladium film 136 is formed on this conductor layer in athickness of approximately 2 μm, and a pattern of resist 99 is formedthereafter. Then, a conductor pattern 132 of the upper-most layer isformed by etching the above-mentioned conductor layer with the resist asa mask.

Next, after a copper film 137 is formed on the whole surface of thesubstrate 135 by a vacuum evaporation method or the like, the resist ispeeled off. With this, as shown in FIG. 9B, it is possible to form thecopper film 137 only on the areas on the surface of the thin filmmultilayer circuit substrate 135 where the palladium film 136 is notformed. Besides, the film thickness of the copper film 137 is made to beapproximately 0.5 μm.

Next, as shown in FIG. 9C, paste obtained by dispersing ultra-fine goldand silver particles each having a particle diameter of approximately 10nm into an organic solvent is applied to the whole surface of thesubstrate 135 by spin coating for instance, thereby to form a conductorpaste film 138 in a thickness of approximately 1 μm.

Next, as shown in FIG. 9D, the substrate 135 and the paste film 138 areheat-treated at approximately 300° C. so as to vaporize the organicsolvent in the paste, and the ultra-fine gold and silver particles aresintered at the same time, thus obtaining a gold-silver alloy film 139.The heat treatment may also be executed in a reduced pressure atmospherein order to prevent air bubbles from generating in the gold-silver alloyfilm 139. The ultra-fine gold and silver particles are sintered easilyby heating at approximately 300° C.

Next, as shown in FIG. 9E, after an adhesive tape 111 is stuck onto thegold-silver alloy film 139, the adhesive tape 111 is peeled off. Then,as shown in FIG. 9F, the gold-silver alloy film 139 that has adheredonto the palladium film 136 remains, but the gold-silver alloy film 139that has adhered onto the copper film 137 is peeled off as it is stuckto the adhesive tape 111. This is because of such a reason that theadhesion of the gold-silver alloy film 139 to the copper film 137 isweak and the gold-silver alloy film 139 can be peeled off easily simplywith the adhesive tape 111, whereas the adhesion of the gold-silveralloy film 139 to the palladium film 136 is strong and the film 139 isnot peeled off easily with the adhesive tape 111.

Then, as shown in FIG. 9G, the copper films 137 at the portions exposedare etched with an ammonium persulfate aqueous solution, thereby toremove the copper films 137 among conductor patterns 140 on the surfaceof the substrate 135. With this, a surface electrode having thegold-silver film 139 on the surface thereof is completed.

According to the present embodiment, complicated processes such asplating pretreatment and plating waste liquid treatment are notrequired, it is possible to form an electrode having a gold-silver filmon the surface thereof easily.

(The tenth embodiment)

FIGS. 10A to 10C are sectional views showing a method of manufacturing asemiconductor device according to a tenth embodiment of the presentinvention.

First, as shown in FIG. 10A, a conductor paste 144 is dropped by anappropriate quantity with a dispenser or the like onto a bonding land142 provided on an aluminum nitride substrate 141. This conductor paste144 is obtained by dispersing ultra-fine metal particles of one metal orseveral metals such as gold, silver, palladium or copper into an organicsolvent such as α-terpineol. Besides, bonding pads 143 are providedaround the bonding land 142 on the surface of the substrate 141.

Next, as shown in FIG. 10B, a semiconductor chip (a bare chip) 145 isplaced with alignment on the bonding land 142. At this time, theconductor paste 144 enters into a gap between the chip 145 and thebonding land 142 by a capillary phenomenon, and the conductor paste 144spreads thinly and uniformly between them. With this, it is possible toplace the chip 145 horizontally with respect to the back of thesubstrate 141. The chip 145 is, for example, a semiconductor chip.

Next, the chip is heated at a temperature of approximately 300° C. in anitrogen atmosphere. With this, as shown in FIG. 10C, the organicsolvent in the conductor paste 144 is vaporized, and fine metalparticles are sintered at the same time, thus forming a metal film 146.The semiconductor chip 145 is fixedly attached firmly to the bondingland 142 by means of this metal film 146, and the bonding land 142 andthe semiconductor chip 145 are connected electrically to each other.

Thereafter, the electrode on the chip 145 and the bonding pads 143 areconnected electrically to each other by bonding wires 147 in a similarmanner as before. With this, bonding or mounting of the semiconductorchip 145 on the substrate 141 is completed.

In the present embodiment, since the conductor paste 144 enters into thegap between the chip 145 and the bonding land 142 by a capillaryphenomenon and spreads thinly and uniformly, the semiconductor chip 145does not incline with respect to the surface of the substrate 141.Further, the present embodiment provides excellent adhesive property,ohmic junction property, heat conduction property and thermal stressabsorption property due to lower temperature bonding, and is alsoapplicable to a wire bonding method for thermal application.Accordingly, such effects that it is possible to aim at simplification,expedience and improvement of reliability of a die-bonding process areobtainable by the method of the present invention.

(The other embodiments)

In the above-mentioned embodiments, paste containing ultra-fine metalparticles is used or solder by electrolytic plating is used as themethod of filling a conductive material constituting the vias in viaholes. As another filling method, a method of filling the ultra-finemetal particles in the via holes by a gas deposition method is used. Thegas deposition method is a method that the ultra-fine metal particlesevaporated in a space at high atmospheric pressure are transported intoa region at low pressure in an aerosol state and injected from a nozzle.

As another method of forming the via holes described above, there is amethod that photosensitive polyimide is used and exposed and developed(and/or cure), thereby to form the via holes. However, it is possible tomake the diameter of the via hole smaller by excimer laser.

In the first to the fourth embodiments, only one via is formed inrespective drawings. However, a plurality of via holes are formedpractically in the multilayer circuit substrate.

What is claimed is:
 1. A method of manufacturing a multilayer circuitsubstrate, comprising the steps of:forming via holes in an insulatingfilm on an under layer; applying an electrically conductive pasteobtained by having ultra-fine metal particles dispersed in a solventonto said insulating film and into said via holes, said ultra-fine metalparticles having a grain size of 5 to 50 nm; and forming vias composedof a sintered product of said ultra-fine metal particles in said viaholes by removing said solvent and also sintering said ultra-fine metalparticles by heating at a temperature of approximately 300° C.
 2. Themethod of manufacturing a multilayer circuit substrate according toclaim 1, wherein interconnections are formed on said insulating film byapplying patterning to the sintered product of said ultra-fine metalparticles that have remained on said insulating film.
 3. The method ofmanufacturing a multilayer circuit substrate according to claim 1,wherein said metal particles are at least one of particles of gold,copper, palladium and nickel, and said solvent is α-terpineol.
 4. Themethod of manufacturing a multilayer circuit substrate according toclaim 1, wherein said sintering is performed in an ambient atmosphere ata pressure lower than the atmospheric pressure.
 5. The method ofmanufacturing a multilayer circuit substrate according to claim 1,wherein said insulating film is formed by curing a photosensitive resin,and said via holes are formed by exposing and developing saidphotosensitive resin.
 6. The method of manufacturing a multilayercircuit substrate according to claim 1, wherein said via holes areformed by irradiation with laser.
 7. The method of manufacturing amultilayer circuit substrate according to claim 1, wherein a lower sideinterconnection is formed under said insulating film and under said viaholes.
 8. A method of manufacturing a multilayer circuit substrate,comprising the steps of:sticking a protective film on an insulatingfilm; forming an opening in said protective film; forming a via hole insaid insulating film under said opening; applying an electricallyconductive paste having ultra-fine metal particles dispersed in asolvent onto said protective film and into said opening and via-hole;heating said electrically conductive paste to remove said solvent and tomake said ultra-fine metal particles into sintered product; and peelingoff said protective film from said insulating film to remove saidsintered product over said insulating film so that said sintered productremains in said via-hole as a via.
 9. The method of manufacturing amultilayer circuit substrate according to claim 8, wherein said metalparticles are at least one of particles of gold, copper, silver,palladium and nickel, and said solvent is α-terpineol.
 10. The method ofmanufacturing a multilayer circuit substrate according to claim 8,wherein said heating is performed in an atmosphere lower than theatmospheric pressure.
 11. The method of manufacturing a multilayercircuit substrate according to claim 8, wherein said heating isperformed at approximately 300° C.
 12. The method of manufacturing amultilayer circuit substrate according to claim 8, wherein said hole isformed by irradiation with laser.
 13. The method of manufacturing amultilayer circuit substrate according to claim 8, wherein the meltingtemperature of said protective film is higher than the sinteringtemperature of said ultra-fine metal particles.
 14. A method ofmanufacturing a multilayer circuit substrate according to claim 8,further comprising the steps of:forming opening portions in saidprotective film along an interconnection forming portion before saidpaste is applied; forming said paste on said insulating film throughsaid opening portions; forming said sintered product of said ultra-finemetal particles on said insulating film by heating said paste on saidinsulating film at the same time when said paste is heated; and forminginterconnections with said sintered product that has remained at tracesof said opening portions by peeling off said protective film from saidinsulating film.
 15. The method of manufacturing a multilayer circuitsubstrate according to claim 8, wherein said protective film is formedof thermoplastic resin.
 16. The method of manufacturing a multilayercircuit substrate according to claim 15, wherein said thermoplasticresin is thermoplastic polyimide.
 17. The method of manufacturing amultilayer circuit substrate according to claim 8, wherein lowerinterconnections are formed under said insulating film and under saidvia hole.
 18. The method of manufacturing a multilayer circuit substrateaccording to claim 8, further comprising a step of forming upperinterconnections passing over said via on said insulating film afterpeeling off the protective film.